A high-performance solar-driven atmospheric water harvester for arid regions based on a self-assembled MOF-on-MOF heterostructure

Efficient freshwater production techniques are urgently required to address the global water-scarcity problem. The solar-driven atmospheric water harvesting (AWH) technology, which can capture water vapour from ambient air and release it under sunlight, is a sustainable and feasible strategy for obtaining fresh water. The key to achieving high water harvesting lays in the dynamic adsorption properties of the material and the heat and mass transfer characteristics of the device structure. Therefore, this paper reports a core-shell structured material, UiO-66@MIL-101(Cr) (U@M), where the outer layer exhibits excellent water-adsorption characteristics under arid conditions, and the inner layer exhibits high water-adsorption characteristics under high humidity conditions. These inner and outer layer materials are assembled into a core-shell structure while considering the water-harvesting features of both sides, achieving synergistic enhancement of the AWH performance at low relative humidity (RH). Experimental results demonstrate that at 25°C and 30 % RH, the novel core-shell structured material achieves a high water-harvesting capacity of 0.408 g g−1 and excellent stability in 50 operating cycle tests. At the system level, we have developed a solar-driven AWH device based on the synthesised core-shell material. Daytime and night-time experimental tests were conducted in outdoor environments, resulting in a water production rate exceeding 1.336 kg m−² day−¹, with the collected water meeting the standards for laboratory-grade pure water. The research findings can be applied to alleviate water issues in arid regions, such as residential water supply, industrial electrolysis for hydrogen production and other fields, showing broad application prospects.